There are many devices that make it possible to maneuver the opening of a curtain. One of the solutions consists in motorizing the movement of the head carriage whereon is fixed an end of the curtain. The head carriage comprises guide wheels, in general, at least two pairs of wheels, running along running tracks formed along a rail fixed in the vicinity of the ceiling of a room.
Applications JP-A-2005-095364 and JP-A-09-327373 describe a head carriage incorporating a friction wheel driven in rotation by a motor and able to be in contact, over a portion of its periphery, with a running surface formed along a rail. The contact force between the friction wheel and the running surface can be adjusted, statically, by a presser means.
DE-A-24 36 753 teaches to take into account the direction of movement of a carriage in order to adjust the contact force of a zone of friction on a rail. Once the direction of movement of the carriage is established, the contact force is independent of the weight of the curtain.
However, during the movement of a curtain, the required force to be provided to the head carriage in order to drive the curtain, changes as it moves. In order to be able to close the curtain, the motor has to be sized in such a way as to be able pull the curtain at the end of travel, i.e., a substantial force proportional to the total mass of the curtain and able to compensate the elastic reaction of the tensioned curtain. At the beginning of a closing maneuver, the head carriage pulls a low load, as the mass of the curtain is supported by static support carriages. Durant this phase, the head carriage only moves a few support carriages and therefore only a few sections of the curtain, which represents a low weight. Then, the head carriage drives more and more support carriages. Consequently, it pulls a higher curtain mass. At the end of travel, the carriage needs to provide a substantial force, in particular proportional to the total mass of the curtain. Therefore, at the beginning of the closing of the curtain, the motor is oversized, which results in a poor output of the device and, therefore, has a negative influence on the consumption of the motor. This disadvantage is even further penalizing when the motor is powered by an autonomous source of energy, the case for which the optimization of the consumption is sought.